1. Field of the Invention
The present invention relates to a magnetic head used on a magnetic recording and reproducing apparatus, and the magnetic recording and reproducing apparatus that uses the magnetic head.
2. Description of the Related Art
Magnetic recording and reproducing apparatuses include a medium for magnetically recording information, a magnetic head for recording the information on and reproducing the information from the medium, a recording and reproducing operation control circuit for reproducing the information based on an output signal from the magnetic head and recording the information based on an input signal, a mechanism for turning the medium, and a positioning mechanism for determining a position of the magnetic head relative to the medium.
A write element constituting the magnetic head includes a coil for generating a magnetic flux, a pair of magnetic cores for collecting the magnetic flux, and a write gap disposed between the pair of the magnetic cores so as to generate a magnetic field. A film formed of a nickel and iron alloy such as Ni80Fe20 or Fe55Ni45, a film formed of an iron and cobalt alloy such as Fe70Co30 or Fe50Co50, a cobalt-based alloy film, or a film formed by stacking approximately two layers of these films are commonly employed for the magnetic cores. A film thickness of each of the cores is often set to approximately 1 to 5 μm in a longitudinal write head. In a perpendicular write head, the film thickness of a main pole is often set to approximately 50 to 200 nm, while the film thickness of a return pole is often set to one to several micrometers. A write operation is performed by applying to the medium the magnetic field generated at the write gap resulting from passage of a write current through the coil.
A read element for the magnetic head includes a pair of magnetic shield layers, a magnetoresistive film interposed between the magnetic shield layers, being apart from a predetermined distance from the magnetic shield layers, and a pair of leads for being electrically coupled to the magnetoresistive film. The pair of magnetic shield layers is present to detect a change in the magnetic field leaked from the medium based on recorded information at high resolution. The narrower a spacing between the pair of shield layers is, the higher resolution can be made. Thus, there is a trend toward the narrower and narrower shield spacing for adapting to a higher recording density of the magnetic recording and reproducing apparatus in the future. In addition to a function described above, the magnetic shield layers also serve to liberate heat that has generated from the magnetoresistive film due to passage of a sensing current, to their outside. The Ni80Fe20 film or an alloy film based on these materials is often employed for the magnetic shield layers. An alloy film such as a Sendust (Fe—Al—Si) film or a cobalt-based amorphous alloy film may also be employed for a shield layer on a substrate side or a lower shield layer. The film thickness of each of the shield layers is generally set to approximately 1 to 5 μm.
In the case of the magnetic recording and reproducing apparatus with an areal density of 100 gigabits per square inch, a high sensitivity sensor such as a GMR film using a giant magnetoresistive effect or a TMR film using a tunneling magnetoresistive effect is employed as the magnetoresitive film.
The GMR film is constituted by a multilayer film that includes a first ferromagnetic layer, a second ferromagnetic layer, and a non-magnetic conductive layer. The first ferromagnetic layer has a thickness of approximately 1 to 10 nm, and its magnetization direction changes, depending on the magnetic field that leaks from the medium. The second ferromagnetic layer has a thickness of approximately 0.5 to 5 nm, and its magnetization direction is generally fixed. The non-magnetic conductive layer is interposed between the first ferromagnetic layer and the second ferromagnetic layer, and has a thickness of approximately 0.5 to 5 nm.
The TMR film is constituted by a: multilayer film that includes the first ferromagnetic layer, the second ferromagnetic layer, and a barrier layer. The first ferromagnetic layer has an approximately 1 to 10 nm in thickness and its magnetization direction changes, depending on the magnetic filed that leaks from the medium. The second ferromagnetic layer has an approximately 0.5 to 5 nm in thickness, and its magnetization direction is generally fixed. The barrier layer is interposed between the first ferromagnetic layer and the second ferromagnetic layer, and has an approximately 0.5 to 1 nm in thickness. The TMR film has a higher sensitivity than the GMR film, though the TMR film has a higher element resistance than the GMR film. Thus, the TMR film is considered to be promising for achieving the higher recording density of the magnetic recording and reproducing apparatus.
In the magnetic recording and reproducing apparatus, by applying the sensing current to these magnetoresistive films described above, an electrical resistance change of the magnetoresistive film is detected as an output (voltage) signal.
In the case of the element that uses the GMR film (hereinafter referred to as a GMR element), a current applying direction is comparatively free; The GMR element of a type where current is applied in the plane of the GMR film has been primarily adopted. For applying current in the plane of the GMR film, there are provided two methods: one is a horizontal current application method where current is passed in a track width direction, and the other is a vertical current application method where current is passed in an element height direction perpendicular to the track width direction. In magnetic disk apparatuses that require a higher sensitivity, almost all magnetic heads adopt the horizontal current application method of passing current in the track width direction. In the case of the vertical current application method where current is passed in the element height direction, there is a need to dispose one of the leads on the side of an air bearing surface. Thus, a sensor unit around the air bearing surface where the sensitivity is the highest cannot be utilized successfully as an output unit, so that required sensitivity cannot be obtained. Accordingly, as a most dominant trend, the leads are disposed horizontally at both trackwidth edges of the GMR film.
However, in the method of applying current in the plane of the GMR film, as a shield-to-shield spacing is narrowed to adapt to the higher recording density of the magnetic recording and reproducing apparatus in the future, insulation between one or both of the shield layers and the magnetoresistive film or insulation between one or both of the shield layers or the leads electrically coupled to the magnetoresistive film is broken due to electrostatic discharge damage or the like. Thus, it becomes more likely that a substantial reduction in an amplitude of a read signal (to almost zero in many cases) or an increase in noise occurs, which leads to a malfunction of the magnetic disk device and a reduction in a magnetic head yield. In order to solve this problem, a CPP (current perpendicular to the plane) mode is proposed. In this method, a pair of the leads is disposed above and below the GMR film so that the sensing current is applied to a film thickness direction of the GMR film.
In this case, the shield layers can also serve as the leads, so that it becomes unnecessary to worry about insulation between one or both of the shield layers and the GMR film, or insulation between one or both of the shield layers and the leads. Further, the CPP mode could increase a magnetoresistive ratio of the GMR film. Accordingly, a CPP-GMR film, together with the TMR film, is considered to be a promising candidate for realizing next-generation high sensitivity magnetic heads.
In the case of the element that uses the TMR film (hereinafter referred to as a TMR element), it is necessary to apply current in the film thickness direction of the barrier layer. Thus, the leads are disposed above and below the TMR film. In this case, one soft magnetic metal can serve as a material for the leads and the shield layer. The TMR element is also one of CPP sensors, so that it is suitable for achieving the narrower shield-to-shield spacing in the future.
In order to reduce a positional deviation between a write position and the magnetoresistive film for a read operation and achieve a higher density of information to be recorded in the magnetic recording and reproducing apparatuses, the magnetic head with their write and read elements stacked on an identical substrate is often employed. In such an integral-type magnetic head, in order to ensure stability and reduce noise during the read operation, a layer of a nonmagnetic film with a submicron film thickness, formed of a material such as alumina, is often inserted between the read and write elements, thereby magnetically separating the read and write elements.
Magnetic separation between the read and write elements in the integral-type magnetic head, however, is not complete. Accordingly, in order to prevent malfunctions of the magnetic recording and reproducing apparatus, the magnetic head has a structure that includes a domain stabilization layer for maintaining the first ferromagnetic layer constituting the magnetoresistive film in a single domain structure state. This is because, even if the domain structure of the first ferromagnetic layer has been disturbed by an influence of the write element, the domain structure of the first ferromagnetic layer can be restored to the single domain structure again due to an effect of the magnetic stabilization layer. When the first ferromagnetic layer is not of the signal domain structure, the amplitude and a shape of a read output waveform change for each write operation, so that the magnetic recording and reproducing apparatus does not operate normally.
It is known that a pair of domain stabilization layers formed of a permanent magnet is disposed at both trackwidth edges of the magnetoresistive film (refer to JP-A-3-125311, for example). In this structure, the first ferromagnetic layer is induced to be in the single domain structure by a magnetic field generated from permanent magnet layers. Use of a multilayer film constituted by ferromagnetic and antiferromagnetic films instead of the permanent magnet layers is also proposed (refer to JP-A-7-57223, for example).
Further, when the magnetoresistive film is the TMR film, there is proposed a structure in which the domain stabilization layer formed of the permanent magnet is stacked on the TMR film (refer to JP-A-11-259824, for example). Still further, there is proposed a structure in which the domain stabilization layer constituted by a multilayer film of the ferromagnetic film and the antiferromagnetic film is stacked on the magnetoresistive film (refer to U.S. Pat. No. 6,023,395, for example).
In order to achieve the higher density of information to be recorded in the magnetic recording and reproducing apparatus, it is necessary to narrow a magnetic track width of the write and read elements of the magnetic head as well as to narrow the shield-to-shield spacing. This is because, by narrowing the shield-to-shield spacing, information can be recorded and reproduced with a high linear recording density. This is also because, by narrowing the track width, information can be recorded and reproduced with a high track density. For achieving an object of narrowing the track width, the distance between the poles of the write element has been primarily narrowed, and the width of the magnetoresistive film and a lead-to-lead spacing have also been narrowed, hitherto.
Further, in order to reduce a crosstalk component in a magnetoresistive-type read element, thereby improving an S/N ratio of the read signal, there is provided a method in which the spacing between the magnetic shield layers in portions with no magnetoresistive film interposed therebetween is reduced to be a half of or narrower than the spacing between the magnetic shield layers in a portion with the magnetoresistive film (Refer to JP-A-6-267027, for example). It is noted in this literature that, by adopting this structure, the crosstalk component of approximately −25 dB in magnitude, resulting from magnetic induction, sensed over a wide range of an entire shield width (typically about 10 to 100 μm in the case of a current magnetic head) can be reduced to a small level of approximately −30 dB. Thus, this structure is described to be effective for improving the S/N ratio.
As described above, for achieving the narrow track width of the read element, the size of the element has been reduced. However, when the magnetic track width of the read element is to be reduced to be less than approximately 100 nm so as to realize the magnetic recording and reproducing apparatus having the areal density exceeding 100 gigabits per square inch, inventors of the present invention have found that, even if the element size is reduced, the magnetic track width is not reduced correspondingly. Accordingly, the inventors have found that the element size needs to be reduced to be considerably smaller than a targeted magnetic track width.
When the width of the magnetoresistive film was set to 100 nm, the shield-to-shield spacing was set to 60 nm, and a magnetic head-to-medium spacing was set to 15 nm, assuming the areal density on the order of 100 gigabits per square inch, for example, a magnetic read track width was approximately 150 nm. Herein the magnetic track width was defined to be the width of locations where an off-track characteristic or a sensitivity distribution of a read head measured by using a signal recorded in a minute recording track becomes 20% (−14 dB) of a maximum output. The sensitivity distribution in this case roughly takes the shape like in a Gaussian distribution.
A difference between the magnetic read track width and the width of the magnetoresistive film is referred to as a side reading. In this case, a large side reading of 50 nm or 50% of the element size was observed. As a result of fabricating heads of various sizes and measuring the off-track characteristic under various conditions, the inventors of the present invention have found that an amount of the side reading is approximately equal to a value obtained by adding the head-to-medium spacing to a half of the shield-to-shield spacing.
In the case where the shield-to-shield spacing is 60 nm and the magnetic head-to-medium spacing is 15 nm, a theoretical side reading becomes as large as approximately 45 nm. Thus, it is found that, in order to obtain the magnetic track width of 100 nm, there is a need to reduce the element size to a minute size of approximately 55 nm. The side reading in this case is approximately 100% of the element size, which is a large value. In a semiconductor industry that has driven a minute pattern formation technique, a technique of mass producing patterns of less than 100 nm has currently been under development. Even with this most-advanced technique, however, it is very difficult to mass produce heads with the track width on the order of 50 nm. In order to realize the magnetic track width on the order of 100 nm, another breakthrough technique is required. Further, the side reading of approximately 45 nm is present in the above-mentioned case, so that it is considered to be almost impossible to realize the magnetic track width equal to or less than 50 nm.
In JP-A-6-267027, for example, there is proposed the method in which the spacing between the magnetic upper and lower shield layers in portions with no magnetoresistive film interposed therebeween is reduced to be a half of or narrower than the spacing between the magnetic upper and lower shield layers in a portion with the magnetoresistive element interposed therebetween. However, the object of the invention described in JP-A-6-267027 is not to provide the magnetic head suitable for a narrow track width, but to improve the S/N ratio by reducing crosstalk noise detected in a wide range over the shield width, as clear from FIG. 2 listed in JP-A-2-57223. As clear from FIG. 2, the magnitude of the crosstalk noise is substantially constant in a width direction of the entire shield layers, which is equivalent to so-called background noise. Accordingly, it is never implied that this crosstalk noise would become a serious problem when the track width of the read element has been narrowed. Hence, the magnetic track width on the order of 100 nm cannot be achieved under current circumstances.
For confirmation, from IEEE Transactions on Magnetics, 1994, vol. 30, pp. 303–308, the size of the read head having been studied at that time will be examined, and a rate of the side reading obtained at that time will be reviewed. According to this paper, the width of the magnetoresistive film was 4000 nm, the shield-to-shield spacing was 420 nm, and the magnetic head-to-medium spacing was 105 nm. The amount of the side reading in this condition is found to be 315 nm in view of a relation described above. This side reading corresponds to as little as 8% of the element size. It shows that, in the case of the magnetic track width on the order of several thousand nanometers, the side reading scarcely became a problem. In other words, the rate of the side reading was small at that time, so that the magnetic track width could be determined almost solely from the element size.
However, as described above, when the track width has been narrowed to be of the order to 100 nm, the narrower the track width becomes, the higher the rate of the side reading becomes. Thus, even if the element size is reduced, the magnetic track width is not reduced so much. Consequently, it has become apparent that, under the current circumstances, realization of the head that accommodates narrower tracks becomes difficult. Further, even if an extremely minute element size was realized with a large side reading and a narrower magnetic track width was then obtained as a result, only an extremely small output can be obtained. It is because the output of the head is roughly proportional to the element size. Thus, it is readily anticipated that the magnetic recording and reproducing apparatus does not operate normally due to insufficient sensitivity.